join_constraints

# File activerecord/lib/active_record/associations/join_dependency/join_association.rb, line 24
        def join_constraints(foreign_table, foreign_klass, join_type, alias_tracker)
          joins = []
          chain = []

          reflection_chain = reflection.chain
          reflection_chain.each_with_index do |reflection, index|
            table, terminated = yield reflection, reflection_chain[index..]
            @table ||= table

            if terminated
              foreign_table, foreign_klass = table, reflection.klass
              break
            end

            chain << [reflection, table]
          end

          base_klass.with_connection do |connection|
            # The chain starts with the target table, but we want to end with it here (makes
            # more sense in this context), so we reverse
            chain.reverse_each do |reflection, table|
              klass = reflection.klass

              scope = reflection.join_scope(table, foreign_table, foreign_klass)

              unless scope.references_values.empty?
                associations = scope.eager_load_values | scope.includes_values

                unless associations.empty?
                  scope.joins! scope.construct_join_dependency(associations, Arel::Nodes::OuterJoin)
                end
              end

              arel = scope.arel(alias_tracker.aliases)
              nodes = arel.constraints.first

              if nodes.is_a?(Arel::Nodes::And)
                others = nodes.children.extract! do |node|
                  !Arel.fetch_attribute(node) { |attr| attr.relation.name == table.name }
                end
              end

              joins << join_type.new(table, Arel::Nodes::On.new(nodes))

              if others && !others.empty?
                joins.concat arel.join_sources
                append_constraints(connection, joins.last, others)
              end

              # The current table in this iteration becomes the foreign table in the next
              foreign_table, foreign_klass = table, klass
            end
          end

          joins
        end